Heating using microwaves (e.g., having frequencies ranging from 300 MHz to 300 GHz) includes dielectric heating based on dielectric loss, which heats a target while causing energy loss in the target, and Joule heating based on induced current, which causes an induced current in a target and heats the target using a resistance component.
FIGS. 1A and 1B are diagrams showing a conventional microwave heating scheme for heating a target in a waveguide.
As shown in FIG. 1A, when a microwave is propagated into a waveguide so as to heat a plate-shaped or film-shaped target within the waveguide, the target may be heated via dielectric heating or joule heating due to the microwave traveling in a z direction in the drawing. In this case, when the width direction of the target is disposed in the z direction in the drawing, it may be assumed that the thickness (x direction) of the target is much smaller than the wavelength of a microwave, and that an electric field generated in a y direction due to the microwave is maintained at a uniform intensity in a Transverse Electric (TE) mode, as shown in FIG. 1B. Accordingly, the heating uniformity of a target may differ depending on the traveling status of the microwave in the z direction. That is, there is a problem in that, when the z direction length of the target becomes greater than ¼ of the wavelength of the microwave, the target is not uniformly heated depending on the locations of the target in the z axis direction.
FIGS. 2A and 2B are diagrams showing the distribution of power transmission depending on the location of a target in the traveling direction of a microwave within a waveguide in a conventional microwave heating scheme.
As shown in FIG. 2A, when the microwave travels along the target, microwave power is attenuated due to the occurrence of power loss depending on the location of the target, and thus a problem also arises in that non-uniform heating occurs due to a difference in power loss depending on the z direction location of the target. In particular, as shown in FIG. 2B, when the wavelength of a microwave (e.g., 12.2 cm) is not much greater than the size of the target (e.g., 4.3 cm×5 cm), the intensity of microwave power loss varies depending on the z direction location of the target, thus causing non-uniform heating.